1/2-13 tap drill size

Drill a 27/64" hole (0.4219" / 10.72 mm) for a 1/2-13 UNC tap. That leaves about 78% thread, the standard for general-purpose tapping.

Tap drill
27/64"
0.4219" · 10.72 mm · 78% thread
Metric drill
10.8 mm 75% thread
Clearance (close)
33/64" 0.5156"
Helicoil (STI) drill
33/64"
1/2-13 tap drill: 27/64" (0.4219 in / 10.72 mm), 78% thread

1/2-13 thread specs

SeriesUnified coarse (UNC)
Major diameter0.5000" (12.70 mm)
Pitch13 TPI (1.95 mm)
Basic minor diameter0.4167" (10.58 mm)
Common internal class2B

Every drill that works for 1/2-13

Drills from all four sets that give 50–85% thread, largest first. Lower percentages tap easier; see how much thread you need.

DrillThreadinmmSetGood for
11.4 mm51%0.448811.40Metricdeep holes only
11.3 mm55%0.444911.30Metricdeep holes only
11.2 mm59%0.440911.20Metricdeep holes only
7/16"63%0.437511.11Fractionalhard or tough metals
11.1 mm63%0.437011.10Metrichard or tough metals
11.0 mm67%0.433111.00Metrichard or tough metals
10.9 mm71%0.429110.90Metricgeneral use
10.8 mm75%0.425210.80Metricgeneral use
27/64"standard78%0.421910.72Fractionalgeneral use
10.7 mm79%0.421310.70Metricgeneral use
10.6 mm83%0.417310.60Metricmore torque, more broken taps

1/2-13 clearance hole

The hole a 1/2-13 screw passes through. Close fit locates parts; free fit is forgiving.

FitDrillinmm
Close fit33/64"0.515613.10
Free fit17/32"0.531313.49

1/2-13 counterbore and countersink

For a socket head cap screw to sit flush, and for a flat head socket screw.

Socket head counterboreDiameterDepth
AMES13/16" 0.8125"0.5000"

Flat head socket screw: countersink at 82° (inch screws, ASME B18.3) to 0.9380" (23.83 mm) across for a flush head. Metric flat heads use 90°, so don't mix countersinks.

1/2-13 holes in a 3D print

Printed holes usually come out undersize. Model the hole at the drill size plus what your printer loses, then tap or drill to size. Why printed holes shrink.

Print a test hole, measure it with calipers, enter the difference. 0 models the nominal size.

Hole to tap
10.72 mm
Clearance hole
13.10 mm

1/2-13 thread repair (Helicoil)

Stripped 1/2-13 thread? Drill out with the STI drill, tap with a 1/2-13 UNC STI tap, and fit a wire thread insert. The drill in your repair kit’s instructions wins over any chart.

ChartSTI drillinmm
AMES33/64"0.515613.10
MISUMI33/64"0.515613.10

Related sizes

3/8-16next size down5/8-11next size up1/2-20fine threadM12closest metricFull chartUNC / UNF

Frequently asked questions

What size drill do I use for a 1/2-13 tap?
Use a 27/64" (0.4219 in / 10.72 mm) drill. It leaves about 78% thread, the standard for general-purpose tapping.
What metric drill can I use for a 1/2-13 tap?
10.8 mm (0.4252 in / 10.80 mm) is the closest, giving about 75% thread. Anything from about 65% to 80% thread taps well in most materials.
What size clearance hole for a 1/2-13 screw?
33/64" (0.5156") for a close fit, 17/32" (0.5313") for a free fit.
What is the metric equivalent of 1/2-13?
M12 is the closest size (12.00 mm vs 12.70 mm major diameter). The pitches differ, so the screws and tapped holes are not interchangeable.

Sources

Spotted a wrong number? Email contact@clove3d.com and it gets fixed.

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% thread = (major − drill) ÷ (1.299 × pitch) × 100. The standard drill comes from published charts and is checked against this formula on every build.